1. Field of the Invention
The present invention relates to an automatic key designating apparatus which is used for an electronic musical instrument.
2. Prior Art
In accordance with the progress in the automatic control technique of the electronic musical instrument, several kinds of automatic accompaniment apparatuses have been developed in these years. This automatic accompaniment apparatus is designed to automatically form additional tones such as duet tones, arpeggio tones, bass tones etc. based on melody performance, chord performance and the like. Then, these additional tones are automatically sounded with chord performance tones and melody performance tones. In this case, it is possible to form the additional tone based on the single chord only. However, in order to form the additional tones suitable for the tune, i.e., suitable for the chord progression, it is desirable to detect the key of the tune to be performed.
Based on such demand, Japanese Patent Laid-Open Publication (i.e., Kokai) No. 57-136696 (corresponding to U.S. Pat. No. 4,419,916) discloses the electronic musical instrument capable of designating the key based on the operations of key designating switches and keys of keyboard prior to the performance (hereinafter, in order to avoid the confusion between "key" and "keys of keyboard", "keys of keyboard" is denoted to as "keyboard-keys"). For example, by simultaneously operating the key designating switch and keyboard keys corresponding to the C tone, it is possible to designate the C key.
However, this conventional apparatus is disadvantageous in that the performer must operate such switch and keyboard-keys to thereby designate the key by himself. Such operation is troublesome for the performer. In addition, in the case where the performer does not know the key of the tune to be performed, it is impossible to designate the key with ease. Further, since such key designation is made by use of the keyboard-keys, it is impossible to designate the key in the middle of the performance. In other words, it is impossible to effect the modulation in the middle of the performance.